This paper provides an overview of recent developments in the science of linguistics, and considers their relevance to the teaching of Spanish in Puerto Rico. First, three significant trends are explained and summarized: (1) structuralism, which emphasizes phonetics, pattern, and distribution, and rejects meaning as a tool of analysis; (2) transformationalism, which assumes the existence of two general linguistic levels, "deep" and "surface," and (3) the study of language acquisition, which attempts to understand the process whereby children achieve fluent control of their native language. Following this broad overview, research findings which have applied linguistics research to Spanish instruction are summarized. Data is described showing that the pervasive loyalty toward Castilian Spanish should be reoriented to develop acceptance of language variations such as regionalism, dialectism, and students' idiolects. Additionally, findings are outlined which suggest that a descriptive attitude and a comprehensive view toward language should take precedence over the prescriptive attitude toward language teaching. Words, it is argued, should be learned in context, by association, and should be functional. Various principles are outlined to support the assertion that Spanish grammar instruction should have a strong theoretical foundation. Finally, among other prescriptions and considerations, teachers are encouraged to develop their own personal philosophy of language teaching. (KH)